Locus-Wide Chromatin Remodeling and Enhanced Androgen Receptor-Mediated Transcription in Recurrent Prostate Tumor Cells

Abstract

Prostate cancers (PCas) become resistant to hormone withdrawal through increased androgen receptor (AR) signaling. Here we show increased AR-mediated transcription efficiency in PCa cells that have acquired the ability to grow in low concentrations of androgen. Compared to androgen-dependent PCa cells, these cells showed increased activity of transiently transfected reporters and increased mRNA synthesis relative to levels of AR occupancy of the prostate-specific antigen (PSA) gene. The locus also displayed up to 10-fold-higher levels of histone H3-K9/K14 acetylation and H3-K4 methylation across the entire body of the gene. Although similar increased mRNA expression and locus-wide histone acetylation were also observed at another kallikrein locus (KLK2), at a third AR target locus (TMPRSS2) increased gene expression and locus-wide histone acetylation were not seen in the absence of ligand. Androgen-independent PCa cells have thus evolved three distinctive alterations in AR-mediated transcription. First, increased RNA polymerase initiation and processivity contributed to increased gene expression. Second, AR signaling was more sensitive to ligand. Third, locus-wide chromatin remodeling conducive to the increased gene expression in the absence of ligand was apparent and depended on sustained AR activity. Therefore, increased AR ligand sensitivity as well as locus-specific chromatin alterations contribute to basal gene expression of a subpopulation of specific AR target genes in androgen-independent PCa cells. These features contribute to the androgen-independent phenotype of these cells.The molecular processes that mediate transcription orchestrate cell proliferation, differentiation, and disease progression. Central to this regulation is the dynamic organization and modification of nucleosomes, the basic repeating unit of chromatin that is comprised of 146 bp of DNA wrapped around histone octamers. Accessibility to transcription factors and activation of genes largely depend on diverse posttranslational modifications of amino termini (36, 47) and the more recently implicated globular domains of histones (6). These modifications include acetylation, phosphorylation, and methylation, which covalently add acetyl, phospho, and methyl groups, respectively, to specific residues of core histones. The well-characterized acetylation and methylation of lysines in histones H3 and H4 are highly correlated with transcriptional activation. Acetylation, catalyzed by histone acetyltransferases such as p300/CBP, is reversed by the activity of histone deacetylases, which mediate transcriptional repression (21). Methylation at histone H3 (K4) is catalyzed by specific methyltransferases often found in large complexes such as ALL-1 (32). This process is reversed by the action of a recently identified lysinespecific histone demethylase, LSD1 (39, 40). The complex interactions between the different histone tail modifications have led to the "histone code hypothesis," which suggests that specific histone modifications affect and interac...

Androgen-Induced Coactivator ANCCA Mediates Specific Androgen Receptor Signaling in Prostate Cancer

“…To extend our analysis to the potential, natural targets of ANCCA, we performed ChIP assay with LNCaP cells stimulated by androgen. As reported previously (23,25,26,40,41), androgenstimulated AR recruitment to the AR-binding regions of IRS-2 (f9 kb downstream of IRS-2 gene), SGK1 (f3 kb upstream of its transcription start site), and PSA genes (Fig. 5B).…”

Androgen receptor and prostate cancer

“…Moreover, in hormone ablation independent prostate cancer cells, chromatin remodeling is conductive to the ligand independent activity of AR. 22 …”

Distinct GCN5/PCAF-containing complexes function as co-activators and are involved in transcription factor and global histone acetylation

“…The role of GCN5-and PCAF-containing complexes in oncogenic gene regulation Aberrations in post-translational modifications of histones have been shown to occur in cancer cells at individual promoters (Barsyte-Lovejoy et al, 2006;Jia et al, 2006). Changes in global levels of histone modifications are also associated with cancer and these changes are predictive of clinical outcome (Seligson et al, 2005).…”